It is known for self-contained computer workstations to be interconnected by a digital network. One advantage of such a network is that users of individual workstations can communicate with one another over the network, for example by means of a typed note, a data file or a program file transmitted to another user. More recently, users have increasingly requested desktop conferencing, remote presentations and other multimedia applications between networked users. However, multimedia applications require high bandwidth communication links between distributed computing systems with minimal communication delay, maximum throughput, and instantaneous burst communication capability. The requirements of multimedia applications make scheduling the appropriate resources difficult.
IBM Technical Disclosure Bulletin (TDB), number 4b, September, 1991, pp. 416-417, Inter-client Resource Usage in Distributed Client Server Presentation Manager System, discloses a distributed client-server presentation system. In such a system, resources, such as cut and paste clipboard, the keyboard, the mouse, etc., are managed across a number of client systems each connected to a display server. The resources are managed by providing generic server functions, neutral to any specific client policies. The Server provides inter-client resource support by managing named "logical resources." Clients use these resources to assign global ownership. For example, assuming a client system, a "FOCUS" resource is created and ownership is acquired by client nodes which require a focus window to receive keyboard input events. The Client requests a resource by name and can request exclusive or shared access. Data can also be associated with a logical resource.
Another IBM TDB, Apr. 4, 1989, p. 349, Managing Serial Use Resources in a Distributed Data Processing System Using an Insertion Ring, discloses a technique which insures that users of serial facilities in a distributed data processing system are properly sequenced. U.S. Pat. No. 5,031,089; Dynamic Resource Allocation Scheme for Distributed Heterogeneous Computer Systems; discloses a similar system for a plurality of networked computer nodes to reallocate system resources for optimized job performance. U.S. Pat. No. 4,747,130; Resource Allocation In Distributed Control Systems; discloses a similar scheduling system for a distributed process control system.
U.S. Pat. No. 4,953,159; Audiographics Conferencing Arrangement; discloses a system for allowing conferees to exchange displayed text and/or graphics stored locally in their respective data terminals. The conferees may change the displayed text and/or graphics and such changes are automatically distributed to the other data terminals so that all of the conferees view the same information.
U.S. Pat. No. 4,389,720; Distributed Digital Conferencing System; discloses a time division communication system for combining those samples going to a particular station forming a conference with combinations of selected time slot samples into a conference sum unique to the station.
Resource reservation must occur at all layers of what is known as the Open Systems Interconnect (OSI) model. At the network layer, a circuit may need to be reserved, for a particular time, through a plurality of intermediate network computer nodes. At the lower layers, the system must ensure that a particular resource managed by the layer can be reserved. At the Medium Access Control (MAC) layer of Fiber Distributed Data Interface (FDDI), a Synchronous FDDI standard of the FDDI Station Manager SMT7.1 describes how a FDDI workstation can communicate bandwidth reservation needs to a plurality of workstations connected to a FDDI ring, and how the negotiated Token holding time and Token Rotation Time can be negotiated by the stations to either grant or deny the bandwidth request of a particular station.
No such standard exists for an IEEE or IBM Token Ring, but there is an architected priority mechanism in the Token Ring and the Token Bus whereby a station on the ting with a high (non-zero) priority frame to send can indicate this in the access control (AC) field of a passing frame, provided that the value of the access field is less than the priority at which the station desires to initialize the AC. When a station sending the frame releases the token, it releases the token at the priority of the AC field, and eventually sets it back to its original priority as specified in the IEEE 802.5 medium access control protocol. The IEEE 802.5 standard and the IBM 802.5 implementation merely specifies the protocol for increasing and decreasing priority, but each station is unconstrained in its use of priority beyond this protocol.
U.S. Pat. No. 5,029,164 describes a network (source to destination) bandwidth reservation algorithm including messages exchanged between source, intermediate and destination nodes. Internet Requests For Comments (RFC) #1190, Experimental Internet Stream Protocol describes a message exchange protocol across a network; like U.S. Pat. No. 5,029,164, RFC 1190 describes message exchanges between a source, destination, and intermediate nodes. But does not solve the specific problems of reserving bandwidth on networks that have shared access and an architected priority mechanism such as the Token Ring.
U.S. Pat. No. 4,587,651 discloses bandwidth reservation on a ring having two network loops, but a slotted, time division multiplexed scheme is used that is unsuitable for asynchronous rings and buses that have architected priority mechanisms for bandwidth reservation, and which lack the necessary physical network clocking required by TDM schemes.
U.S. Pat. No. 5,050,161 describes a scheduling system in source, destination and intermediate computer network nodes which can provide throughput, delay and delay jitter (variation in delay) guarantee. But this patent requires that all packets having a certain quality of service guarantees be assigned a time slot which is unique to the station (it is not TDM, time division multiplexed) and transmitted at the start of the time slot. This scheme requires that connections be identified and is thus not suitable for the medium access control layer which does not recognize connections; it does not contain arbitration among a plurality of computer network nodes sharing a common transmission medium, such as a Token Ring, and it does not specify how priority can be used to implement bandwidth reservation on a shared transmission medium.
Prior to this invention, no means existed for allowing Token Ring priority to guarantee bandwidth and delay times.